The present invention relates to a magnetic video recording and reproducing system (VTR), and more particularly to a color killer circuit thereof.
A color killer circuit has been well known which detects the presence or absence of a burst signal in a video signal to deactivate a color signal processing circuit and expand a pass band of a luminescence signal processing circuit when a monochromatic video signal is to be recorded or reproduced in order to assure high fidelity recording and reproduction of monochromatic and color video signals.
Heretofore, the color killer circuit in the magnetic video recording and reproducing system (VTR) usually detects a level of the burst signal in the carrier chrominance signal, rectifies it to produce a d.c. voltage which is compared with a threshold level to produce a LOW output or HIGH output, which is used to control the color killer operation. Such a prior art color killer circuit, however, has problems in that the burst level changes depending on a variance of the levels of the burst signals transmitted from different broadcasting stations or by a distortion in a transmitted electromagnetic wave and that the color killer circuit operates improperly due to the influence of noise in a weak electric field strength region such that the monochromatic signal is erroneously determined as the color signal or vice versa. It has a further problem in that because of a difference between the threshold level of the color killer circuit in the recording system and that in the reproducing system in the VTR or a difference between the sensitivities of video heads, the color signal recorded is reproduced as a monochromatic signal if the burst level is low.